MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA (LD78) EXPRESSED IN HUMAN BONE-MARROW - ITS ROLE IN REGULATION OF HEMATOPOIESIS AND OSTEOCLAST RECRUITMENT

Human macrophage inflammatory protein-1 alpha (hMIP-1 alpha), also kno wn as LD78, is a member of the chemokine/intercrine family and an inhi bitor of the proliferation of the hematopoietic stem cells in vitro. U sing a specific monoclonal antibody, we observed significant localizat ion of hMIP-1 alpha in eosinophilic myelocytes in human bone marrow. W e further examined the expression of hMIP-1 alpha or mRNA in human bon e tissue by in situ hybridization. A high level of hMIP-1 alpha mRNA e xpression was detected in eosinophilic myelocytes in bone marrow, conf irming these cells as the site of hMIP-1 alpha synthesis. hMIP-1 alpha mRNA expression was also detected in osteoblasts in the bone-remodeli ng sites, and osteoclasts were frequently observed in the vicinity of these osteoblasts. hMIP-1 alpha was also able to induce osteoclastogen esis on calcified matrices in the absence of any other osteotropic hor mones. These results strongly suggest that hMIP-1 alpha is involved no t only in the regulation of hematopoiesis but also in the modulation o f bone remodeling.